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Engineering of surface microstructure transformations using high rate severe plastic deformation in machining

机译：在加工中利用高速率严重塑性变形进行表面微观结构转变的工程

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摘要

Engineering surface structures especially at the nanometer length-scales can enable fundamentally new multifunctional property combinations, including tunable physical, mechanical, electrochemical and biological responses. Emerging manufacturing paradigms involving Severe Plastic Deformation (SPD), for manipulating final microstructure of the surfaces are unfortunately limited by poorly elucidated process-structure-performance linkages, which are characterized by three central variables of plasticity: strain, strain-rate and temperature that determine the resulting Ultrafine Grained (UFG) microstructure. The challenge of UFG surface engineering, design and manufacturing can be overcome if and only if the mappings between the central variables and the final microstructure are delineated.;The objective of the proposed document is to first envision a phase-space, whose axes are parameterized in terms of the central variables of SPD. Then, each point can correspond to a unique microstructure, characterized by its location on this map. If the parametrization and the population of the datasets are accurately defined, then the mapping is bijective where: i) realizing microstructure designs can be reduced to simply one of tuning process parameters falling within the map s desired subspaces. And, inversely, ii) microstructure prediction is directly possible by merely relating the measured/calculated thermomechanics at each point in the deformation zone to the corresponding spot on the maps.;However, the analytic approach to establish this map first requires extensive datasets, where the microstructures are accurately measured for a known set of strain, strain-rate and temperature of applied SPD. Although such datasets do not exist, even after the empirical data is accumulated, there is a lack of formalized statistical outlines in relating microstructural characteristic to the process parameters in order to build the mapping framework. Addressing these gaps has led to this research effort, where Large Strain Machining (LSM) is presented as a controlled test of microstructure response. Sample conditions are created using LSM in Face Centered Cubic (FCC) metals, while characterizing the deformation using Digital Image Correlation(DIC) and Infrared(IR) thermography. Microstructural consequences such as grain size, subgrain size and grain boundary responses resulting from the characterized thermomechanical conditions are examined using Electron Back-Scattered Diffraction (EBSD). Once empirical data is generated across the broad thermomechanical conditions, reliable microstructure maps are populated. This characterization can help understand surface microstructures resulting from shear-based manufacturing processes such as turning, milling, shaping, etc. that are created under analogous thermomechanical conditions.;Keywords: microstructure characterization, ultrafine grain microstructure, severe plastic deformation, high speed deformation.
机译：工程表面结构，特别是纳米级尺度的表面结构，可以从根本上实现新的多功能特性组合，包括可调的物理，机械，电化学和生物响应。不幸的是，涉及到严重塑性变形（SPD）的新兴制造范例用于操纵表面的最终微观结构受到工艺-结构-性能关联性不佳的限制，这些关联性的特征在于可塑性的三个主要变量：应变，应变率和温度，它们决定了塑性。产生的超细晶粒（UFG）显微组织。只有且仅当描绘出中心变量和最终微观结构之间的映射时，才能克服UFG表面工程，设计和制造的挑战。拟议文件的目的是首先设想一个相空间，其轴已参数化就SPD的中心变量而言。然后，每个点都可以对应一个唯一的微结构，其特征在于它在该图上的位置。如果准确定义了数据集的参数化和总体，则映射是双射的，其中：i）可以将实现微结构设计的过程简化为仅属于映射所需子空间的调整过程参数之一。反之，ii）通过仅将变形区域中每个点处的测量/计算出的热力学与地图上的对应点相关联，就可以直接进行微观结构预测;然而，建立该地图的分析方法首先需要大量的数据集，其中对于已知的应变，应变速率和所施加SPD的温度，可以精确地测量微结构。尽管不存在这样的数据集，但是即使在积累了经验数据之后，也缺乏将微观结构特征与过程参数相关联以建立映射框架的形式化统计轮廓。解决这些差距导致了这项研究工作，其中提出了大应变加工（LSM）作为微结构响应的受控测试。使用LSM在面心立方（FCC）金属中创建样品条件，同时使用数字图像相关（DIC）和红外（IR）热像图表征变形。使用电子背散射衍射（EBSD）检查了特征热力学条件导致的微观结构后果，例如晶粒尺寸，亚晶粒尺寸和晶粒边界响应。一旦在广泛的热机械条件下生成了经验数据，便会生成可靠的微观结构图。这种表征可以帮助理解在类似热机械条件下产生的基于剪切的制造工艺（例如车削，铣削，成形等）产生的表面微观结构。关键词：微观结构表征，超细晶粒微观结构，严重的塑性变形，高速变形。

著录项

  • 作者

    Abolghasem, Sepideh.;

  • 作者单位

    University of Pittsburgh.;

  • 授予单位 University of Pittsburgh.;
  • 学科 Industrial engineering.;Nanotechnology.;Mechanical engineering.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 138 p.
  • 总页数 138
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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